Wooden barrels have been used for centuries to age and store liquor and wine. In fact at the present time, almost 50% of all wine produced is still being aged in 60 gallon oak barrels. Almost all of whiskey has been traditionally aged in smaller 50 gallon oak barrels.
The wine industry has grown, and presently more wine is aged in barrels than at any other time in history. There are estimates of close to ten times as many barrels used in the production of wine as there was in the late 1980's. Because wine is aged in barrels for upward of four years before it is ready to be bottled and consumed, there is a growing demand for oak wine barrels. To solve the problem of where and how to store all of the wine barrels, and to keep up with the growing demand, the portable steel barrel rack was developed in the late 1970's. Throughout the years as the barrel racks were adopted in the wine cellars, the racks evolved through a series of changes, shapes, and sizes ending with the modern rack most commonly used today. These modern racks enable the wineries to vertically stack one to six levels of a module (barrel rack with from two to four barrels placed on top) on a floor area of less than ten square feet. These barrel racks are designed to be easily moved and stacked with a fork lift truck. In addition, the racks accommodate easy barrel service, which includes racking the wine (removal of solids), topping off the barrels to replace evaporated liquids, and washing the barrels for future use.
As a direct result of the experience of some of the major wineries in California during two severe earthquakes of the mid and late 1980's, a growing number of wineries have developed concerns with the height they are stacking their barrels. Since the modules are independently stacked one on top of another, heights of more than 18 feet can be reached in a typical six module barrel stack; see FIGS. 1-3.
There are two reasons for this concern. One is personal safety for the many wine cellar workers who service the barrels each day. The other is the potential financial loss of the wine due to damaged and destroyed barrels. The typical wine barrel is made up of wooden staves shaped into a bulging cylinder contained by six to eight steel hoops spaced along the length of the barrel, a flat circular head at both ends, at least one bung hole generally on the belly, and the bung or cork. The barrels weigh from about 125 to 140 pounds empty and up to approximately 625 pounds full. A filled barrel of wine is valued at an average of $2200 based on an average price of $37 per gallon.
Although California wineries in the Santa Cruz Mountains, Monterey, and the south San Francisco Bay Area suffered great damage due to the 1984 Morgan Hill earthquake and the 1989 Loma Prieta 7.1 earthquake, it has only been within the past couple of years that an extensive investigation has been undertaken to learn if and how such damage could be alleviated.
A portion of the earthquake damage calculation was due to barrels stacks toppling which in turn caused the barrels to break and/or the bungs to pop loose allowing wine to leak on to the cellar floor. The damage the wineries experienced in these two past earthquakes is significantly less than what could be experienced in an earthquake today. This is true partly because of the greater number of oak barrels that are stored on these modern barrel racks stacked to heights of up to 18 feet. The wine industry was much smaller in the 1980's and the industry did not have a problem of limited storage space. Therefore the wineries had no need to be stacking the barrels at heights that could be considered unsafe. The investigation has shown that many of the wineries who were using the modern barrel rack system experienced barrel and wine losses due to wine barrels from the top-most module being ejected and thrown to the cellar floor. The investigation included interviews with personnel that were present in wine cellars during and after a severe earthquake to observe the affect the seismic shaking had on the barrel stacks. In addition, a study of the complex behavior of a barrel stack subjected to an earthquake was made possible by designing laboratory shake table tests described in the Example Section below.
In view of the foregoing, there is a need in the wine industry for a solution to the problem of protecting all of the barrels in a barrel stack of the type of module described above against damage from earthquakes.